Clinical question: Which risk factors are key in the development of non-leg deep vein thromboses (NLDVTs), and what are the expected clinical sequelae from these events?

Background: Critically ill patients are at increased risk of venous thrombosis. Despite adherence to recommended daily thromboprophylaxis, many patients will develop a venous thrombosis in a vein other than the lower extremity. The association between NLDVT and pulmonary embolism (PE) or death is less clearly identified.

Study design: The PROphylaxis for ThromboEmbolism in Critical Care Trial (PROTECT), a multicenter, randomized, blinded, and concealed prospective cohort study occurring between May 2006 and June 2010.

Setting: Sixty-seven international secondary and tertiary care ICUs in both academic and community settings.

Synopsis: Researchers enrolled 3,746 ICU patients in a randomized controlled trial of dalteparin versus standard heparin for thromboprophylaxis. Of these patients, 84 (2.2%) developed a NLDVT. These thromboses were more likely to be deep and located proximally.

Risk factors were assessed using five selected variables: APACHE (acute physiology and chronic health evaluation), BMI, malignancy, and treatment with vasopressors or statins. Outside of indwelling upper extremity central venous catheters, cancer was the only independent predictor of NLDVT.

Compared to patients without any VTE, those with NLDVT were more likely to develop PE (14.9% versus 1.9%) and have longer ICU stays (19 versus nine days). On average, one in seven patients with NLDVT developed PE during the hospital stay. Despite the association with PE, NLDVT was not associated with an increased ICU mortality in an adjusted model. However, the PROTECT trial may have been underpowered to detect a difference. Additional limitations of the study included a relatively small total number of NLDVTs and a lack of standardized screening protocols for both NLDVT and PE.